U.S. patent application number 14/380329 was filed with the patent office on 2015-01-22 for fiber reinforced elastomeric stator.
The applicant listed for this patent is Smith international, Inc.. Invention is credited to Peter Thomas Cariveau, Scott Meng.
Application Number | 20150022051 14/380329 |
Document ID | / |
Family ID | 49006194 |
Filed Date | 2015-01-22 |
United States Patent
Application |
20150022051 |
Kind Code |
A1 |
Meng; Scott ; et
al. |
January 22, 2015 |
Fiber Reinforced Elastomeric Stator
Abstract
Embodiments disclosed herein relate to a composition useful for
forming stator or a portion thereof. The composition may include: a
curable elastomer; a fiber fibrous compound; a fiber dispersion
compound; and optionally carbon black.
Inventors: |
Meng; Scott; (Houston,
TX) ; Cariveau; Peter Thomas; (Spring, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Smith international, Inc. |
Houston |
TX |
US |
|
|
Family ID: |
49006194 |
Appl. No.: |
14/380329 |
Filed: |
February 21, 2013 |
PCT Filed: |
February 21, 2013 |
PCT NO: |
PCT/US2013/027098 |
371 Date: |
August 21, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61601445 |
Feb 21, 2012 |
|
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|
Current U.S.
Class: |
310/216.001 ;
29/596; 524/493; 524/514 |
Current CPC
Class: |
B29C 45/0053 20130101;
B29L 2031/749 20130101; Y10T 29/49009 20150115; H02K 1/12 20130101;
F05C 2253/04 20130101; E21B 4/02 20130101; F04C 2/1075 20130101;
B29C 45/0001 20130101; H02K 15/02 20130101; C08L 9/02 20130101;
C08L 2205/16 20130101; F04C 13/008 20130101; C08K 7/02 20130101;
F03C 2/08 20130101 |
Class at
Publication: |
310/216.001 ;
29/596; 524/514; 524/493 |
International
Class: |
C08L 9/02 20060101
C08L009/02; H02K 1/12 20060101 H02K001/12; H02K 15/02 20060101
H02K015/02 |
Claims
1. (canceled)
2. (canceled)
3. (canceled)
4. (canceled)
5. (canceled)
6. (canceled)
7. (canceled)
8. (canceled)
9. (canceled)
10. (canceled)
11. The composition of claim 19, wherein the curable elastomer
comprises at least one of NBR and HNBR and has a Mooney Viscosity
(ML(1+4) at 121.degree. C.) in the range from about 20 to about
120.
12. The composition of claim 19, wherein the composition comprises:
from about 75 to about 99 wt. % curable elastomer; from about 1.25
to about 1.75 phr aramid fiber; from about 0.5 to about 15 phr
amorphous silicon dioxide; and from about 10 to about 100 phr
carbon black.
13. A method of forming a stator or a portion thereof, comprising:
admixing a curable elastomer, a fiber, and a fiber dispersion
compound to form a curable composition; disposing the curable
composition in a mold; and curing the curable composition to form a
stator liner or portion thereof having randomly dispersed
fiber.
14. The method of claim 13, wherein the admixing comprises mixing
the curable elastomer with a predispersion comprising the fiber and
the fiber dispersion compound.
15. (canceled)
16. A drilling motor, comprising: a stator, the stator having a
stator liner with at least one elastomeric layer formed at least
partially from a composition including a curable elastomer, a
fiber, and a fiber dispersion compound; and a rotor, the rotor
being configured to rotate eccentrically when a drilling fluid is
passed through the motor; wherein the composition includes from
about 0.5 to about 1.8 phr fiber, where phr is defined as parts per
hundred parts curable elastomer, and the fiber dispersion compound
is selected from the group consisting of a solid fiber dispersion
compound, a liquid fiber dispersion compound, or mixtures
thereof.
17. (canceled)
18. (canceled)
19. A composition useful for forming a fiber reinforced elastomeric
component useful in oilfield products, such as a seal or a stator
liner, the composition comprising: a curable elastomer; a fiber,
wherein the composition comprises from about 0.5 to about 1.8 phr
fiber, where phr is defined as parts per hundred parts curable
elastomer; and a fiber dispersion compound selected from the group
consisting of a solid fiber dispersion compound, a liquid fiber
dispersion compound, or mixtures thereof.
20. The composition of claim 19, wherein the fiber dispersion
compound comprises a solid fiber dispersion compound comprising a
nanometer or micrometer sized spherical structure.
21. The composition of claim 19, wherein the solid fiber dispersion
compound comprises at least one of amorphous silicon dioxide, an
alumina silicate, a silica aluminate, a magnesium silicate, coal
dust, and silicon dioxide powder.
22. The composition of claim 19, wherein the solid fiber dispersion
compound comprises amorphous silicon dioxide having an average
particle size in the range from about 30 nm to about 300 nm and a
surface area in the range from about 10 m.sup.2/g to about 30
m.sup.2/g.
23. The composition of claim 19, wherein the liquid fiber
dispersion compound comprises at least one of a liquid polymer, a
processing aid, a wax, and a plasticizer.
24. The composition of claim 19, wherein the composition comprises
from about 1 to about 1.8 phr fiber.
25. The composition of claim 19, wherein the composition comprises
from about 1.25 to about 1.75 phr fiber.
26. The composition of claim 19, wherein the fiber comprises at
least one of carbon fibers, boron fibers, ceramic fibers, glass
fibers, thermoplastic fibers, natural fiber, metallic fibers, and
synthetic fibers.
27. The composition of claim 19, wherein the fiber comprises an
aramid fiber.
28. The composition of claim 19, wherein the curable elastomer
comprises at least one of NBR, HNBR, FKM, FEPM, and FFKM.
29. The composition of claim 19, further comprising carbon
black.
30. (canceled)
31. (canceled)
32. (canceled)
33. The drilling motor of claim 16, wherein the composition further
includes carbon black.
34. The drilling motor of claim 16, wherein the fiber dispersion
compound includes amorphous silicon dioxide.
35. The method of claim 13, wherein carbon black is also admixed to
form the curable composition.
36. The method of claim 13, wherein the fiber dispersion compound
includes amorphous silicon dioxide.
Description
FIELD OF THE DISCLOSURE
[0001] Embodiments disclosed herein relate generally to stators
used with positive displacement drilling motors. More specifically,
embodiments disclosed herein relate to a fiber reinforced stator,
and compositions for forming the fiber reinforced stator, wherein
the fiber is easily incorporated and well dispersed throughout the
elastomeric matrix.
BACKGROUND
[0002] Moineau style hydraulic motors and pumps are conventional in
subterranean drilling and artificial lift applications, such as for
oil and/or gas exploration. Such motors make use of hydraulic power
from drilling fluid to provide torque and rotary power, for
example, to a drill bit assembly. While downhole drilling motors
fall into the general category of Moineau-type motors, they are
generally subject to greater working loads, temperatures, and more
severe chemical and abrasive environments than Moineau motors and
pumps used for other applications. As such, the demands on drilling
motor components (rotor and stator components) typically far exceed
the demands on the components of other Moineau-type motors and
pumps. For example, drilling motors may be subject to a pressure
drop (from top to bottom across the motor) of up to 1500 psi at
temperatures of up to about 200.degree. C. Furthermore, a
conventional stator may exceed 25 feet in length. Achieving
suitable processability (e.g., flowability) in order to injection
mold the elastomer materials tends to be difficult at such lengths.
Moreover, many rubber compounds are known to deteriorate in the
presence of hydrocarbons.
[0003] The power section of a typical Moineau style motor includes
a helical rotor disposed within the helical cavity of a
corresponding stator. When viewed in circular cross section, a
typical stator shows a plurality of lobes in the helical cavity. In
most conventional Moineau style power sections, the rotor lobes and
the stator lobes are preferably disposed in an interference fit,
with the rotor including one fewer lobe than the stator. Thus, when
fluid, such as a conventional drilling fluid, is passed through the
helical spaces between rotor and stator, the flow of fluid causes
the rotor to rotate relative to the stator (which may be coupled,
for example, to a drill string). The rotor may be coupled, for
example, through a universal connection and an output shaft to a
drill bit assembly. Rotation of the rotor therefore causes rotation
of the drill bit in a borehole.
[0004] One drawback with conventional stators including an all
elastomer helical cavity component is that a tradeoff in elastomer
properties has been required. One such tradeoff has been between
the resilience (rigidity) of the elastomer and its processability
(its flowability during injection molding). For example, U.S. Pat.
No. 6,905,319 to Guo states: "processability is generally inversely
related to the stiffness of the rubber. This is particularly true
in injection-mold processes . . . . Typically, a stiffer compound
will demand much more processing power and time, thereby increasing
manufacturing costs" (column 4, lines 4-12). Despite the potential
advantages of using a stiffer elastomer, Guo discloses an elastomer
having a hardness of about 74 on the Shore A scale (ASTM D2240).
Guo's teaching is consistent with conventional wisdom in the art,
which suggests that rigid elastomers (e.g., those having a Shore A
hardness of about 90 as well as other mechanical properties
described in more detail below) are not suitable for use in
downhole stators due to inherently poor processability. The
elastomeric materials in conventional stators typically have a
hardness (Shore A) in the range from 65-75.
[0005] One significant drawback with conventional stators is that
the elastomer helical cavity component deforms under torque loads
(due to the low rigidity of the elastomer). This deformation
creates a gap on the unloaded side of the stator lobe, thereby
allowing drilling fluid to pass from one cavity to the next without
producing any work (i.e., without causing rotation of the rotor).
This is known in the art as "RPM drop-off." When the torque reaches
a critical level, substantially all of the drilling fluid bypasses
the stator lobes and the rotor stalls. Thus, flexibility of the
liner may lead to incomplete sealing between the rotor and stator
such that available torque may be lost when the rotor compresses
the stator lobe material, thereby reducing the power output of the
PDM.
[0006] Additional problems may be encountered with stators when,
for example, rotation of the rotor within the stator shears off
portions of the stator lobes. This process, which may be referred
to as "chunking," deteriorates the seal formed between the rotor
and stator and may cause failure of the PDM. Chunking may be
increased by swelling of the liner or thermal fatigue. Swelling and
thermal fatigue may be caused by elevated temperatures and exposure
to certain drilling fluids and formation fluids, among other
factors.
[0007] Various attempts have been made to increase stator
durability and heat conduction properties. For example, U.S. Pat.
No. 6,102,681, issued to Turner, describes fibers disposed in an
elastomer material that forms a stator of a helicoidal pump or
motor. The fibers are arranged to form a two or three dimensional
structure within the elastomer material. The fibers are either
coated with the elastomer material as they are being woven to form
a fabric layer or are formed into the desired arrangement to form a
fiber skeleton. After the fiber skeleton is formed, elastomer is
then injected into the stator under heat and pressure to complete
the process. Other processes for forming a stator having a fiber
reinforced layer may include one or more of U.S. Pat. No.
7,950,914, U.S. Pat. No. 7,739,792, U.S. Pat. No. 7,517,202, U.S.
Pat. No. 7,083,401; U.S. Pat. No. 6,604,921, U.S. Pat. No.
6,183,226, U.S. Pat. No. 5,759,019, US20090169404, US20110116959,
US20110116960, US20110116961, and US20030192184, among others.
[0008] Fiber reinforcement, to date, has presented significant
manufacturing difficulties as it is difficult to achieve desired
stator properties using injection molding techniques, such as due
to due to fiber settling or agglomeration, poor dispersion of the
fiber throughout the elastomeric matrix, excessive viscosity of the
elastomeric composition when incorporating the fibers (i.e., poor
processability or a very limited processing window unsuitable for
injection molding processes at the fiber loadings necessary to
achieve the desired properties), among other shortcomings. The poor
dispersion of the fiber via such processes impairs the elastomeric
compound static and dynamic properties as well as performance
consistency. As a result, fiber reinforcement via injection molding
requires additional costly and labor-intensive manufacturing steps,
such as weaving or placement of the fibers or a fibrous mat within
or around a mold, and the manufacturing processes generally produce
either a different concentration of fibers per unit volume of
elastomer between the thick portions of the lobes and the thin
portions (which reduces the mechanical strength of the liner) or,
when fibers are disposed manually, a different number of layers
must be applied in the thick portions of the lobes as compared to
the thin portions. Due to the aforementioned reasons, fiber
reinforced elastomeric stators have not been commercially
successful.
SUMMARY OF THE DISCLOSURE
[0009] A novel method has now been developed to disperse aramid
fibers or other fibers into an elastomeric matrix via injection
molding or extrusion molding, overcoming one or more of the above
noted deficiencies. It has been found that improved processability
and dispersion of fibers throughout an elastomeric matrix may be
achieved by admixing fibers and a fiber dispersion compound, such
as amorphous silicon dioxide, with an elastomeric material. It is
theorized, for example, that the highly spherical geometry of the
amorphous silicon dioxide provides a physical bearing effect, and
as a result, the processability of the admixture and incorporation
of a limited amount of the fiber and interaction of the fiber with
the elastomeric matrix are greatly improved.
[0010] In one aspect, embodiments disclosed herein relate to a
composition useful for forming a stator or a portion thereof. The
composition may include: a curable elastomer; a fiber; a fiber
dispersion compound; and carbon black. The composition may include
from about 0.5 to about 1.8 phr fiber, where phr is defined as
parts per hundred parts curable elastomer
[0011] In another aspect, embodiments disclosed herein relate to a
method of forming a stator or a portion thereof, the process
including: admixing a curable elastomer, from about 0.5 to about
1.8 phr fiber, a fiber dispersion compound; and carbon black to
form a curable composition; disposing the curable composition in a
mold; curing the curable composition to form a stator liner or
portion thereof.
[0012] In another aspect, embodiments disclosed herein relate to a
stator useful in positive displacement drilling motors, the stator
including: a stator liner comprising at least one elastomeric layer
comprising a curable composition comprising: a curable elastomer,
from about 0.5 to about 1.8 phr fiber, a fiber dispersion compound;
and carbon black, or a reaction product thereof.
[0013] In another aspect, embodiments disclosed herein relate to a
drilling motor, comprising: a stator and a rotor, the rotor being
configured to rotate eccentrically when a drilling fluid is passed
through the motor; wherein the stator comprises a stator liner
comprising at least one elastomeric layer comprising a curable
composition comprising: a curable elastomer, from about 0.5 to
about 1.8 phr fiber, a fiber dispersion compound; and carbon black,
or a reaction product thereof.
[0014] In another aspect, embodiments disclosed herein relate to a
drilling assembly, comprising: a drilling motor comprising a stator
and a rotor configured to rotate eccentrically when a drilling
fluid is passed through the motor, the stator and rotor each having
a proximal end and a distal end, and wherein the stator comprises a
stator liner comprising at least one elastomeric layer comprising a
curable composition comprising: a curable elastomer, from about 0.5
to about 1.8 phr fiber, a fiber dispersion compound; and carbon
black, or a reaction product thereof; a motor output shaft directly
or indirectly coupled to the distal end of the rotor; and a drill
bit directly or indirectly coupled to a distal end of the motor
output shaft. In another aspect, embodiments disclosed herein
relate to a method of drilling a wellbore through a subterranean
formation, the method comprising passing a drilling fluid through
the drilling assembly.
[0015] In another aspect, embodiments disclosed herein relate to a
composition useful for forming a fiber reinforced elastomeric
component useful in oilfield products, such as a seal or a stator
liner, the composition comprising: a curable elastomer; from about
0.5 to about 1.8 phr fiber; and a fiber dispersion compound.
[0016] In another aspect, embodiments disclosed herein relate to a
method of forming a fiber reinforced elastomeric component useful
in oilfield products, such as a seal or a stator liner, comprising:
admixing a curable elastomer, from about 0.5 to about 1.8 phr
fiber, and a fiber dispersion compound to form a curable
composition; disposing the curable composition in a mold; curing
the curable composition to form the fiber reinforced elastomeric
component. In another aspect, embodiments disclosed herein relate
to a fiber reinforced elastomeric component, useful in oilfield
products, comprising the curable composition or a reaction product
thereof.
[0017] Other aspects and advantages will be apparent from the
following description and the appended claims.
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIG. 1 shows a cross-sectional view of a rotor useful in mud
motors according to embodiments disclosed herein.
[0019] FIG. 2 shows a cross-sectional view of a stator according to
embodiments disclosed herein.
[0020] FIG. 3 shows a cross-sectional view of an assembled positive
displacement motor according to embodiments disclosed herein.
[0021] FIG. 4 shows a cross-sectional view of an assembled positive
displacement motor according to embodiments disclosed herein,
having an "even-wall" stator liner.
[0022] FIGS. 5-8 compare the physical properties of stators
according to embodiments herein to stators without fiber.
DETAILED DESCRIPTION
[0023] In one aspect, embodiments disclosed herein relate generally
to stators used with positive displacement drilling motors. More
specifically, embodiments disclosed herein relate to a fiber
reinforced stator, and compositions for forming the fiber
reinforced stator, wherein the fiber is easily incorporated and
well dispersed throughout the elastomeric matrix.
[0024] Referring to FIG. 1, a typical rotor 10 includes at least
one lobe 12 (wherein, for example, channels 14 are formed between
lobes 12), a major diameter 8, and a minor diameter 6. The rotor 10
may be formed of metal or any other suitable material. The rotor 10
may also be coated to withstand harsh drilling environments
experienced downhole.
[0025] Referring to FIG. 2, a stator 20 according to embodiments
herein comprises at least two lobes 22, a major diameter 7, and a
minor diameter 5. Rotor 10 (FIG. 1) typically includes "n" lobes,
and the corresponding stator 20 used in combination with the rotor
10 generally includes either "n+1" or "n-1" lobes. Referring to
FIG. 3, the stator 20 generally includes a cylindrical external
tube 24 and a liner 26. The liner 26 is typically injected or
extruded into the cylindrical external tube 24 around a mold (not
shown) that has been placed therein. The liner 26 is then cured for
a selected time at a selected temperature (or temperatures) before
the mold (not shown) is removed. A thickness 28 of the liner 26 is
generally controlled by changing the dimensions of the mold (not
shown). A curing pressure, temperature, and time may be selected
using means know in the art so as to completely cure the elastomer.
After completion of the curing process, the stator will be returned
to normal atmospheric conditions. Final machining may be required
to complete the stator (e.g., ends of the liner may need to be
trimmed, ends of the stator may be threaded, etc.).
[0026] As illustrated in FIG. 2, liner 26 has a non-uniform
thickness. In other embodiments, "even-wall" stators may be formed
using fiber reinforced compositions disclosed herein, such as
illustrated in FIG. 4. Positive displacement motor (PDM) 30
comprises a stator 32 and a rotor 34. The stator 32 comprises an
external tube 38 that may be formed from, for example, steel or
another material suitable for downhole use in a drilling
environment. The stator also comprises a liner 36. The external
tube 38 comprises a shaped inner surface 44 that comprises at least
two lobes 46 formed thereon. The lobes 46 are helically formed
along a selected length of the external tube 38 so that the lobes
46 define a helical pattern along the selected length. The helical
form of the inner surface 44 generally corresponds to a desired
shape for stator lobes. The liner 36 typically comprises at least
two lobes 40, and a thickness 42 of the liner 36 may be either
uniform or non-uniform throughout a cross-section thereof, and
formed by injection molding, extrusion molding or other means
followed by curing and finishing, as noted above. The lobes 40 (and
the liner 36) are helically formed along a selected length of the
external tube 38 such that the liner 36 conforms to the helically
shaped inner surface 44 so that the at least two lobes 46 formed on
the shaped inner surface 44 correspond to the lobes 40 formed in
the liner 36. The external tube 38, including the inner surface 44,
may be helically shaped by any means known in the art including
machining, hydroforming, extrusion, and the like.
[0027] Stator liners according to embodiments disclosed herein may
be formed from a fiber reinforced elastomeric or polymeric
material. In other embodiments, stator liners may include a
composite structure, such as an elastomeric layer and one or more
fiber reinforced layers intermediate the external tube (housing)
and the elastomeric outer layer. The intermediate fiber reinforced
layer(s) may provide additional stiffness and/or wear resistance of
the liner.
[0028] Stator liners, portions of stator liners, or reinforcing
layers thereof, may be formed from a composition including: [0029]
a. a curable or cross-linkable elastomeric or polymeric material,
such as various elastomers, polymers, and other synthetic or
natural materials known in the art; [0030] b. a fiber or fibrous
material; [0031] c. a fiber dispersion compound; and [0032] d.
carbon black. The compositions used to form stator liners or
portions thereof may also include plasticizers, curatives (i.e.,
curing or crosslinking agents), activators, processing aids, and
waxes.
[0033] The curable elastomeric materials may include, for example,
G.R.S., NEOPRENE, butyl and nitrile rubbers, fluorinated or
perfluoro elastomers or rubbers, and soft PVC, among other
polymers. In some embodiments, the elastomeric compound may include
one or more of NBR, HNBR, FEPM, FKM, and FFKM.
[0034] In some embodiments, the elastomeric material may include a
copolymerization product of 1,3-butadiene and acrylonitrile having
a Mooney Viscosity ML(1+4) at 121.degree. C. in the range from
about 20 to about 120. The acrylonitrile content may be in the
ranges from about 19 wt. % to about 49 wt. %, and the hydrogenation
may be full or partial, leaving a residual double bond content from
less than 1% to about 18%.
[0035] In other embodiments, the elastomeric material may be a
copolymer of vinylidene fluoride and hexafluoropropylene having a
Mooney Viscosity ML(1+10) at 100.degree. C. in the range from about
10 to about 160. In some embodiments, the fluorine content of the
elastomeric material may be in the range from about 60 to about
70%.
[0036] Elastomeric materials may also be a copolymer of vinylidene
fluoride, hexafluoropropylene, and tetrafluoroethylene, with or
without a cure site monomer, having a Mooney Viscosity ML(1+4) at
121.degree. C. in the range from about 25 to about 65.
[0037] In other embodiments, the elastomeric material may be a
copolymer of tetrafluoroethylene and propylene, with or without a
cure site monomer, having a Mooney Viscosity ML(1+4) at 100.degree.
C. in the range from about 35 to about 160. In some embodiments,
the fluorine content of the elastomeric material may be in the
range from about 55 to about 65%.
[0038] The aforementioned polymers may be used alone or in
combination with one or more additional polymers or grades of a
similar polymer at a ratio in the range from about 20:80 to about
80:20.
[0039] The fiber or fibrous material may include at least one of
carbon fibers, boron fibers, ceramic fibers, glass fibers,
thermoplastic fibers, natural fiber, metallic fibers, synthetic
fibers, and carbon nanotubes. For example, in some embodiments the
fibers may include fibers made from E-glass, polyethylene PEI,
PVDC, PTFE, PVDF, PVF, EFP, PEEK, PPS, and PEI. In some
embodiments, the fiber or fibrous material may include aramid
fibers, such as those sold under the mark "KEVLAR" (a mark of E.I.
DuPont de Nemours of Wilmington, Del.).
[0040] Aramid fibers useful in some embodiments herein may have an
average diameter in the range from about 0.5 to about 25 microns in
some embodiments; from about 1 micron to about 20 microns in other
embodiments; and from about 5 microns to about 15 microns, such as
about 12 microns, in yet other embodiments. The fibers may have a
length in the range from about 1 mm to about 50 mm in some
embodiments; from about 5 mm to about 40 mm in other embodiments;
and from about 10 mm to about 30 mm, such as about 20 mm, in yet
other embodiments. Aramid fibers may have an aspect ratio (length
to diameter) in the range from about 1:1 to about 300:1 in some
embodiments, and from about 1:1 to about 200:1 in other
embodiments. The aramid fibers may have a tensile strength of over
500,000 psi and be able to withstand temperatures of up to about
400.degree. C.
[0041] In some embodiments, fiber reinforced stator liners, or the
layers/portions of a stator liner that are fiber reinforced, may
include up to about 2 wt % fiber, such as in the range from about
0.5 to about 1.8 phr, based on the total amount of elastomeric
compound, in some embodiments, from about 1 to about 1.8 phr in
other embodiments, and from about 1.25 to about 1.75 phr in yet
other embodiments. In other embodiments, the fiber may be present
in an amount from a lower limit of about 0.5, 0.6, 0.7, 0.8, 0.9,
1.0, 1.1, 1.2, 1.3, 1.4, 1.5, or 1.6 phr to an upper limit of about
1.2, 1.3, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, or 1.8 phr,
where any lower limit may be combined with any upper limit.
[0042] While it has been proposed to add significantly greater
quantities of fiber, such as 10 phr or greater, it has been found
that incorporation of fibers in quantities less than about 1.8 phr,
such as from about 1.5 to about 1.75 phr, may provide an optimal
balance of significant improvements in physical properties, as well
as excellent improvements in stator torque output capacity and
stator endurance at high torque levels, with minimal negative
impact on the compound resilience, elasticity, dispersity, and
processability. It is theorized that greater quantities of fiber
may result in discontinuities or imperfections in the elastomer
matrix, possibly due to inefficient dispersion of the fiber at
higher concentrations, which may result in little or no improvement
in stator performance.
[0043] Fiber dispersion compounds are defined herein as compounds
that facilitate the incorporation of the fiber with the elastomeric
material, and may include solid dispersion compounds, liquid
dispersion compounds, or combinations thereof. One example of a
solid fiber dispersion compound useful in embodiments disclosed
herein may include amorphous silicon dioxide. In some embodiments,
amorphous silicon dioxide having an average particle size in the
range from about 0.03 microns to about 0.3 microns (30 nm to 300
nm) and a surface area in the range from about 10 to about 30
m.sup.2/g, such as about 20 m.sup.2/g, may be used as a fiber
dispersion compound. It is theorized that the relatively spherical
amorphous silicon dioxide particles may provide a bearing effect
and a viscosity-lowering effect on the resulting admixture of the
fibers with the elastomeric material, allowing for improved
processability of the elastomeric mixture and improved dispersion
of fibers throughout the resulting elastomeric matrix upon cure.
Other solid fiber dispersion compounds, such as nano or micron
sized spherical structures that may provide similar
viscosity-reducing and bearing effects may also be used, and may
include various natural and synthetic clays (alumina silicates,
silica aluminates, etc.), magnesium silicates, coal dust, and/or
silicon dioxide powder. Liquid dispersion compounds that may be
useful in embodiments herein may include liquid polymers, waxes,
and various processing aids or plasticizers.
[0044] In some embodiments, incorporation of the fiber into the
curable composition mixture may be facilitated by use of a
predispersion of fiber in a fiber dispersion compound. For example,
a mixture of 5 wt. % to about 70 wt. % fiber in 95 wt. % to about
30 wt. % fiber dispersion compound may be admixed with an
elastomeric material prior to injection or extrusion molding of the
curable composition in a mold. In some embodiments, the fiber
dispersion compound may be used in an amount ranging from about 0.5
to about 36 phr, such as from about 0.5 to about 15 phr in other
embodiments. In other embodiments, the fiber dispersion compound
may be present in an amount from a lower limit of about 0.5, 0.6,
0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, or 2.0 phr
to an upper limit of about 1.25, 1.5, 1.75, 2.0, 2,5, or 5 phr,
where any lower limit may be combined with any upper limit.
[0045] In some embodiments, curable compositions useful for forming
a stator liner or a portion/layer thereof may be formed by
admixing: [0046] a. a curable or cross-linkable elastomeric or
polymeric material, such as various elastomers, polymers, and other
synthetic or natural materials known in the art; [0047] b. a fiber
or fibrous material in an amount ranging from about 0.5 to about
1.8 phr (based on the total amount of component a) predispersed in
a fiber dispersion compound (c); [0048] c. the fiber dispersion
compound in an amount ranging from about 0.5 to about 36 phr;
[0049] d. optionally, carbon black in an amount ranging from about
10 to about 100 phr; [0050] e. optionally, one or more curatives
and/or activators, each in an amount ranging from about 1 to about
50 phr.
[0051] In other embodiments, curable compositions useful for
forming a stator liner or a portion/layer thereof may be formed by
admixing: [0052] a. a curable or cross-linkable elastomeric or
polymeric material, such as various elastomers, polymers, and other
synthetic or natural materials known in the art; [0053] b. an
aramid fiber in an amount ranging from about 1 to about 1.8 phr
(based on the total amount of component a) predispersed in
amorphous silicon dioxide as fiber dispersion compound (c); [0054]
c. amorphous silicon dioxide (fiber dispersion compound) in an
amount ranging from about 1 to about 12 phr; [0055] d. carbon black
in an amount ranging from about 10 to about 100 phr; [0056] e.
optionally, one or more curatives and/or activators, each in an
amount ranging from about 1 to about 50 phr.
[0057] The above described curable compositions may be formed using
a screw mixer, a BANBURY mixer, a single or multiple screw
extruder, or other mixing devices as known in the art for
intimately mixing a polymeric or elastomeric resin material with
one or more additive compounds. The mixing process may further
provide heat, melting the polymeric or elastomeric resin material
during the mixing process, and the resulting fluid mixture may then
be extruded, injected, or otherwise disposed between a stator tube
(housing) and a mold that has been placed therein. The liner
material may then be cured and the stator finished (trimming,
threading, etc.), as described above.
[0058] It has been found that the curable compositions according to
various embodiments herein are processable using injection molding
equipment (used in about 90% of the current stator manufacturing
processes). Further, it has been found that the unique combination
of fiber, fiber dispersion compounds, and carbon black allows for
uniform fiber dispersion and pronounced property improvements to be
achieved. A uniform fiber density is advantageous because it helps
achieve, for example, uniform wear resistance throughout the
thickness of the liner. A uniform fiber density is particular
desirable proximate the lobes because the lobes experience the
highest mechanical and thermal stresses. Additional support and
wear resistance proximate the lobes help increase the longevity of
the liner. Note that, in some embodiments, the liner thickness is
at a maximum proximate the lobes, and a uniform fiber density
supports and helps stiffen these regions so as to reduce
deformation of the lobes caused by, for example, fluid pressure and
contact with the rotor. Such results were heretofore unattainable
with random fiber placement/orientation methods, as much higher
fiber loadings were required to compensate for the agglomeration
and non-uniformity of the fiber displacement, negatively impacting
elongation properties, tear strength, compression set, and other
dynamic properties affecting stator life and sealing performance.
Additionally, the high fiber loadings typical of prior methods
result in a compound viscosity spike and drastic changes to
compound cure characteristics, making such mixtures unsuitable for
some manufacturing processes, including injection molding
processes. Embodiments of curable compounds disclosed herein
overcome these deficiencies, resulting in an improved stator and a
simplified manufacturing process.
[0059] As noted above, curable compositions disclosed herein may
provide for improved processability using injection molding
tooling. For example, NBR and other elastomeric compounds having a
Mooney Viscosity ML(1+4) at 121.degree. C. in the range from about
25 to about 40, and in some embodiments up to about 50, may be
preferred when forming the stator via injection molding equipment
typically used to produce stators having a length in the range from
about 10 to about 25 feet (from about 3 to about 7.5 meters).
Compositions useful with extrusion molding may include elastomeric
compounds having a Mooney Viscosity ML(1+4) 100.degree. C. in the
range from about 25 to about 65, and in some embodiments up to
about 80. Compositions useful with compression molding may include
elastomeric compounds having a Mooney Viscosity ML(1+4) 100.degree.
C. in the range from about 25 to about 90, and in some embodiments
up to about 120. Compositions useful with transfer molding may
include elastomeric compounds having a Mooney Viscosity ML(1+4)
100.degree. C. in the range from about 20 to about 45.
[0060] The above described stators may be used in a mud motor or
drilling assembly used for the drilling of a wellbore through a
subterranean formation. A lower end of the rotor may be coupled
either directly or indirectly to, for example, a drill bit. In this
manner, the PDM provides a drive mechanism for a drill bit
independent of any rotational motion of a drill string generated
proximate the surface of the well by, for example, rotation of a
rotary table on a drilling rig. Accordingly, PDMs are especially
useful in drilling directional wells where a drill bit is connected
to a lower end of a bottom hole assembly (BHA). The BHA may
include, for example, a PDM, a transmission assembly, a bent
housing assembly, a bearing section, and the drill bit. The rotor
may transmit torque to the drill bit via a drive shaft or a series
of drive shafts that are operatively coupled to the rotor and to
the drill bit. In operation, a drilling fluid is passed through the
mud motor assembly, eccentrically rotating the rotor as the
drilling fluid passes through the progressive cavity motor. The
motor output shaft transmits the eccentric rotor motion (and
torque) to the concentrically rotating drill bit to drill the
formation.
EXAMPLES
TABLE-US-00001 [0061] TABLE 1 Formula 1 Formula 3 (comparative)
Formula 2 (comparative) Polymer 100 100 100 Carbon Black 90 90 75
Plasticizer 20 20 20 40% Fiber predispersion 0 4 15 Curatives 5.5
5.5 5.5 Activators 11 11 11 Total 226.5 230.5 226.5
TABLE-US-00002 TABLE 2 Formula 1 Formula 2 Formula 3 ASTM D412-06
Tensile (psi) 2100 1900 1300 Elongation (%) 300 250 70 Mod at 25%
200 800 800 ASTM D624-00 260 230 230 Tear Die C Tstrength (lbf/in)
Tstrength (lbf/in) after 72 200 220 hr water immersion at
300.degree. F. ASTM D395 (22 hrs at 35 37 65 250.degree. F.)
Compression Set % ASTM D429 90 degree 90 120 Adhesion Peel (lbf/in)
Adhesion Peel (lbf/in) after 15 30 72 hr water immersion at
300.degree. F. RPA (30 mins at 300.degree. F.) ML 0.29 0.29 MH 15
15
[0062] Table 1 is a side-by-side formulation comparison, on the
basis of adding the fibers into the same formulation with equal
total phrs, Formula 1 (comparative example, typical of commercially
available stators) has no fibers, Formula 3 (comparative example)
has about 6 phr aramid fiber (predispersed in amorphous silicon
dioxide); and Formula 2 (according to embodiments herein), includes
about 1.6 to 1.7 phr aramid fibers (predispersed in amorphous
silicon dioxide). Table 2 compares the physical properties of the
resulting materials upon cure. The stiffness improvement, over the
comparative example without fibers, in 25% modulus is around 400%
while other properties show minimal change, such as elongation,
compression set, and ML. This is due to excellent uniformity of
fiber dispersion obtained by the current method and the optimal
fiber phrs so that fiber achieves a synergistic interaction with
the carbon black at a very low loading of 1.7 phr to boost the
modulus. The disadvantage of high fiber loading is apparent in
formula 3 that the compound has a dramatic loss of elongation and
compression set values goes up significantly. On the other hand,
the low loading of fiber thereby renders minimal impact to other
properties. Further, the fiber is high in surface area and high in
aspect, which increases the interaction between fiber/CB and
polymer matrix, giving rise to an enhanced high temperature
performance and high bond strength between the rubber and
adhesive.
[0063] FIGS. 5 through 8 graphically compare the physical
properties of the composition of Formula 1 (comparative) to that of
Formula 2. As noted above and illustrated in FIG. 5, the 25%
modulus for the cured composition based on Formula 2 is
significantly greater than that for Formula 1 (greater than 800 psi
vs. less than 200 psi). FIGS. 6 and 7 illustrate the differences in
peel strength and tear strength, both prior to and subsequent to
immersion in water at 300.degree. F. for 72 hours, simulating
downhole operating conditions. With regard to peel strength,
Formula 2 showed improvements both before and after immersion. Tear
strength for Formula 2 was less than that for Formula 1 before
immersion, but under simulated downhole conditions showed marked
improvement as compared to Formula 1.
[0064] FIG. 8 compares stator performance for stators formed from
Formula 1 (NBR reg) and Formula 2 (NBR Fiber). The performance test
was performed on a 6.25 inch long section of a stator having an
external diameter of 7/8 inch using a simulated drilling fluid. The
stators were formed using the same mold and tested under the same
test procedure. The pressure drop of the test stator was set to 300
psi per stage after the warm-up and initial tests and the motor
output (rpm and torque) were measured over time. The test was
stopped upon failure of the stator. The rpm of the stators was
roughly equivalent, which is expected based upon the differential
pressure per stage. The initial torque output for the stator with
fiber (Formula 2) was greater and decreased at a slower rate over
time. Endurance of the stator based on Formula 2 was significantly
greater, as shown on the graph. Further, filtering of the stator
effluent drilling fluid during testing showed significantly less
chunking and flaking of polymeric material from the stator of
Formula 2 as compared to the stator of Formula 1.
[0065] As described above, embodiments disclosed herein provide for
a novel method for uniformly dispersing fibers in an elastomeric
matrix. In addition to the above noted advantages with respect to
uniform fiber density, improved processability in the manufacture
of stators, embodiments disclosed herein may also provide for mud
motors having improved durability and/or power generation. For
example, the fibers may serve to strengthen and stiffen the
elastomer of the stator so that it is better able to withstand a
certain amount of degradation in properties without failure or
chunking and can operate with less interference with the rotor
without leakage.
[0066] In addition to stator manufacture, compositions disclosed
herein may also be useful for manufacturing fiber reinforced seals
and other fiber reinforced oilfield equipment. For example, the
benefits realized by use of a fiber predispersion, such as a
mixture of aramid fibers in amorphous silicon dioxide, may improve
the manufacturing process and/or resulting properties of seals and
other fiber reinforced oilfield equipment. The effective dispersion
and synergistic effects realized with the fiber and fiber
dispersion compound in combination with carbon black may also
benefit various fiber reinforced oilfield equipment. Accordingly,
seals, stator liners, and other oilfield products or portions or
reinforcing layers thereof, may be formed from according to
embodiments disclosed herein using a composition including: [0067]
a. a curable or cross-linkable elastomeric or polymeric material,
such as various elastomers, polymers, and other synthetic or
natural materials known in the art; [0068] b. a fiber or fibrous
material; [0069] c. a fiber dispersion compound; and [0070] d.
optionally carbon black. The compositions used to form seals and
other oilfield product or portions/layers thereof may also include
plasticizers, curatives (i.e., curing or crosslinking agents),
activators, processing aids, and waxes.
[0071] While the disclosure includes a limited number of
embodiments, those skilled in the art, having benefit of this
disclosure, will appreciate that other embodiments may be devised
which do not depart from the scope of the present disclosure.
Accordingly, the scope should be limited only by the attached
claims.
* * * * *